Field of the Invention
Such a device is known, for example, from WO 2011/057675. The DC voltage switch explained therein has an operating current path comprising a mechanical switch and a disconnection branch, which is connected in parallel with the operating current path. A series circuit comprising power semiconductor switches is arranged in the disconnection branch, with in each case one freewheeling diode being connected in opposition in parallel with said power semiconductor switches. The switching units consisting of power semiconductor switches and freewheeling diode are arranged back-to-back in series, wherein the power semiconductor switches which can be switched off are arranged in series and a corresponding power semiconductor switch with opposite forward direction is provided for each power semiconductor switch. In this way, the current can be interrupted in both directions in the disconnection branch. In the operating current path, furthermore active commutation means are arranged in the configuration of an electronic auxiliary switch. During normal operation, an operating current flows via the operating current path and therefore via the closed mechanical switch since the power semiconductor switches of the disconnection branch represent an increased resistance for the direct current. In order to interrupt a short-circuit current as fault current, for example, the electronic auxiliary switch is transferred to its off position. As a result, the resistance in the operating current path increases, and therefore the direct current commutates into the disconnection branch. The quick-action mechanical switch disconnector can therefore be opened in the deenergized state. The short-circuit current passed via the disconnection branch can now be interrupted by the power semiconductor switches. In order to absorb the energy stored in the DC voltage grid and to be decayed during switching, diverters are provided, which are connected in parallel with the power semiconductor switches of the disconnection branch.
In addition to such an active power electronics commutation device, DC voltage switches have been described in which the commutation of the total current takes place owing to the arc voltage of the mechanical switch which is arranged in the operating current path. It is also known that a power electronics component part in the disconnection branch can provide active commutation. In this case, the power electronics component part in the mesh formed from the operating current path and the disconnection branch generates a circulating current, which is in opposition to the operating or fault current in the operating current path. In the switch, the two currents are superimposed on one another to give zero given corresponding driving of the power semiconductors so that the switch can be opened in the deenergized state. For such active commutation, the power semiconductor switches need to provide a high power very quickly since the current increases very quickly in the event of a short circuit.